Composite article made by a process

ABSTRACT

Disclosed herein is a consolidated or densified composite article comprising polymer, particularly fluoropolymer, and carbon fiber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalApplication No. 61/222,728, filed Jul. 2, 2009; U.S. ProvisionalApplication No. 61/222,702, filed Jul. 2, 2009; U.S. ProvisionalApplication No. 61/222,743, filed Jul. 2, 2009; U.S. ProvisionalApplication No. 61/222,754, filed Jul. 2, 2009; and U.S. ProvisionalApplication No. 61,222,770, filed Jul. 2, 2009.

FIELD OF THE INVENTION

The field of the invention encompasses a process for the production ofcomposites containing reinforcing fiber and a polymer, particularlycomprising carbon fiber and fluoropolymer.

BACKGROUND OF THE INVENTION

Composite articles comprising or consisting of a polymer (usually acontinuous phase, and possibly comprising fluoropolymer(s) and fibers(such as glass fibers, carbon fibers, and graphite fibers) are wellknown in the art. The addition of fiber to a matrix polymer can improvecertain properties of the polymer. These properties can include creepresistance, tensile strength and modulus, and flexural strength andmodulus. The reinforcing fiber chosen generally has a higher tensilemodulus and strength than the polymer alone. When a fluoropolymer isused as the matrix polymer, as described herein, the resulting compositeoften has many of the attributes of fluoropolymers such as hightemperature resistance and chemical resistance, which make suchcomposites useful as parts, for example, for the chemical processingindustry. It is among the objects of this invention to provide a methodfor the production of such polymer composites that exhibit improvedproperties and to provide articles made by the method.

Background information regarding producing composites of polymer andfiber or fibers can be found in Polymeric Materials Encyclopedia, byJoseph C. Salamone (Jul. 23, 1996), ISBN-10: 084932470X, ISBN-13:978-0849324703 pages 8327-8343.

Some background in double-belt press lamination is found in “Modellingof heat transfer in thermoplastic composites manufacturing: double-beltpress lamination” by A. Trende, B. T. Astrom, A. Woginger, C. Mayer, M.Neitzel, in Composites Part A: Applied Science and Manufacturing, Volume30, Issue 8, August 1999, Pages 935-943.

Known related methods and articles include but are not necessarilylimited to U.S. Pat. No. 5,470,409 to Deakyne et al., issued Nov. 28,1995, entitled “Process for making fluoropolymer composites,” U.S. Pat.No. 5,232,975 to Deakyne, issued Aug. 3, 1993, entitled“Preconsolidation process for making fluoropolymer composites,” U.S.Pat. No. 4,163,742 to Mansure, issued Aug. 7, 1979, entitled “Processand product prepared from tetrafluoroethylene polymer and graphitefibers,” U.S. Pat. No. 5,427,731 to Chesna et al., issued Jun. 27, 1995,entitled “Compression molding of structures,” and U.S. Pat. No.7,011,111 to Spiegl et al., issued Mar. 14, 2006, entitled “Sealingelements for compressor valves”.

Additional known related methods and articles include but are notnecessarily limited to U.S. Pat. No. 5,759,927 to Meeker, issued Jun. 2,1998, entitled “Glass-fiber-containing non-woven polymer web, andprocess for preparing same,” and U.S. Pat. No. 5,460,764 to Held, issuedOct. 24, 1995, entitled “Method and apparatus for making highlydensified sheets”.

There remains a need for any one or combinations of improvements inthese fields, including but not limited to: a simplified process ofmanufacture; a robust and/or reproducible process of manufacture thatcan produce robust and/or reproducible product; a process to produce anarticle of increased density; an article of increased density; a processto produce products having fewer metal, metallic, ionic, or relatedimpurities, particularly for processes that include a solvent or water;a process for using fibers that preserves fiber length; a process toproduce product having a uniform property throughout a useful volume;any process to produce a composite product having a directional property(such as tensile strength, compressive strength, or elongation to break)that is uniform or superior regardless of the direction of measurement(or uniform or superior in one direction, or uniform or superior in twoorthogonal directions), and the like.

These improvements are sought in areas where composite articles areused, e.g. equipment for semiconductor manufacture, in aircraft parts,in automotive parts, in gaskets, in seals, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically some mattes of the known art.

FIG. 2 shows elevation views of a matte and two composite articlesaccording to the present disclosure.

SUMMARY OF THE INVENTION

Disclosed herein is a composite article having a density, Dc, andcomprising: (i) polymer having a softening temperature and (ii) fibers,said composite article made by:

providing a matte, comprising: from about 1 wt % to about 90 weightpercent of said fibers; and from about 10 weight percent to about 90weight percent particles of said polymer, said matte having a density,Dm, that is less than Dc;

densifying said matte to a compressed density greater than 1.1 times Dmand less than 0.999 times Dc while at least a portion of said matte isat a temperature less than softening temperature of polymer, to providea compressed matte;

heating said compressed matte throughout to a temperature greater thansaid softening temperature at a density greater than 1.1 times Dm andless than 0.999 times Dc, to provide a preconsolidated matte; cooling atleast a portion of said preconsolidated matte to a temperature less thansaid softening temperature, to provide a consolidated matte;

stacking a plurality of said consolidated matte to provide an article;

compressing the height of said article and heating throughout to atemperature greater than said softening temperature, to provide aconsolidated composite article; and

cooling at least a portion of said consolidated composite article to atemperature less than said softening temperature.

DETAILED DESCRIPTION OF THE INVENTION

Disclosed herein is a method for making a composite article of densityDc comprising polymer and fibers. The method disclosed herein comprisesproviding a matte comprising: about 1 to about 91 weight percent fiberand about 9 to about 99 weight percent of said polymer. The matte has adensity of Dm, and is less than Dc, wherein said polymer has a softeningtemperature. The matte is densified by compressing the matte to a thatis density greater than 1.1 times Dm and less than 0.999 times Dc, whileat least a portion of the matte is at a temperature less than saidsoftening temperature, to provide a compressed matte. Thereafter thecompressed matte is heated throughout to a temperature greater than saidsoftening temperature while at a consolidated density greater than 1.1times Dm and less than 0.999 times Dc, to provide a pre-consolidatedmatte.

At least a portion of the pre-consolidated matter is cooled to atemperature less than said softening temperature, to provide aconsolidated matte. The next step is stacking heightwise a plurality ofthe consolidated matte to provide an unconsolidated article. Theunconsolidated article is then consolidated by compressing the height ofsaid unconsolidated article and heating it throughout to a temperaturegreater than said softening temperature, to provide a consolidatedcomposite article. At least a portion of the consolidated compositearticle is cooled to a temperature that is less than said softeningtemperature.

In certain embodiments, the invention can combine elements known to theart in a new manner to achieve one or more unexpected or unpredictableresults, including, possibly, unexpected or unpredictable combinationsof results. Single elements of such art may include U.S. Pat. No.5,506,052, 6,066,395, 20090062426, 7,094,468, 7,150,913, 5,589,055,4,420,512, 4,975,321, 4,555,446, 5,227,2385, 4,448,910, 4,455,343,20070082199, 6,444,187, 4,448,911, or 5,236,982 or combinations thereof;the disclosure of all of which is incorporated herein by reference.

Density of composite articles can be determined by ASTM D 792-08Standard Test Methods for Density and Specific Gravity (RelativeDensity) of Plastics by Displacement. Thickness of mattes can bedetermined by TAPPI T411 Thickness (Caliper) of Paper, Paperboard andCombined Board, and weight per volume can be determined by cutting anarea of known size (e.g. 16 cm by 16 cm) and thickness as determined byTAPPI T411, and weighing that known volume of matte.

A typical matte of polymer flake or particles and fibers (17 of FIG. 1Aor 17′ of FIG. 1B) or a composite article may have a density of about0.2 g/mL or less to about 1.9 g/mL or more, depending somewhat on theweighted density of the polymer and fibers used, A typical consolidatematte of polymer flake, or particles, combined with fibers (17′″ of FIG.1C) should have a density greater than the matte it was made from, andmay have a density of about 0.3 g/mL to about 2.9 g/mL, dependingsomewhat on the weighted density of the polymer and fibers used. FIGS.1A-D represent the prior art and aid in the understanding the invention.FIG. 1A shows a matte 17 comprising polymer particles 102 and fibers 101situated between two platens 60,62. Release films 61,63 can optionallybe placed between two platens 60, 62 and the matte 17 composed of fibers101 and polymer particles 102, or the platens can optionally otherwisebe treated to prevent sticking of the matte to a platen. The matte 17can optionally be initially under low contact pressure from the platensas heat is applied to the mattes, for example through the platens. Thepolymer particles will soften and typically change shape upon exceedingthe softening temperature of the polymer. FIG. 1B illustrates a mattethat can be obtained as the temperature exceeds the softeningtemperature and as the formation of beads 102 on (optionally wetting)the fibers within the layer 17′. Not all the original polymer particlesneed be heated above their softening temperature. Pressure can beapplied to platens 60,62 causing the height of the matte to decrease(optionally densifying or compressing it) as illustrated in FIG. 1C forthe change in density, for a matte densified throughout at a temperatureuniformly higher than the polymer softening temperature to give aconsolidated matte 17″. The matte as illustrated is in a relativelyunconstrained state at the edges of the platens, i.e., in the in-planedirections, therefore the fibers can be moved, along with the polymer,in those directions, giving the fibers an arrangement more perpendicularto the height direction of the matte (the height direction being the zdirection) and more parallel to the platen surfaces.

Since the polymer-fiber mix can be unconstrained in-plane during anydensification, there need be no compression forces perpendicular to thez axis, and buckling need not occur. The consolidated matte canoptionally be cooled under pressure, particularly to below the softeningtemperature. This same sequence of events can be achieved on acontinuous basis using a heated belt press or similarly a heating zoneand nip rolls. The process can include the polymer being heated abovethe softening temperature at some point; this can occur before or afterthe application of pressure that produces significant densification. Thecomposite can be cooled under pressure.

Belt press pre-consolidation matte or (debulked plies) result in a veryflat product versus the incumbent platen presspre-consolidated/debulking ply method. Very flat plies eases the abilityto load debulked plies for molding steps.

Significant densification is meant to describe densification to adensity less than or equal to a desired density and yet equal to or morethan 10% greater than initial density. For example, if initial densityof a matte is about 0.586 g/mL and the desired density of a compositearticle made from a single matte or a stack of such mattes is 2.1 g/mL,then 50% densification for a preconsolidated matte is a density of0.586+[0.50*(2.1−0.586)]=1.343 g/mL.

A consolidated matte 17″ of FIG. 1C can be further consolidated as aboveto form a more densified matte or composite article 17′″ of FIG. 1D. Theapparatus used for further consolidation may be the same or differentthan that used for the initial densification.

FIG. 2 shows elevation views of an oriented matte and two compositearticles comprising such oriented mattes. FIG. 2A shows an orientedmatte 2001; for clarity, fibers are shown as imbedded. A coordinate axisset x-y-z 2002 is defined so that the height of the matte is orientedparallel to the z axis. Since fibers 2003 are aligned, on average, alongone direction perpendicular to the z axis, one can assign that directionto correspond to the x axis. Perpendicular to z and x axes is the yaxis.

The matte illustrated in FIG. 2A has been cut from a larger matte, tomake two cut faces (2006 and 2007) parallel to the z axis, and parallelto the y and x axes respectively. By such cutting, an observer can notethat fibers 2004 can be cut with relatively circular cross section bythe xz face 2006, and fibers 2005 can be cut with relatively ellipticalcross section (or ultimately nearly a parallelogram) by the xz face2006.

FIG. 2B shows a portion of an oriented composite article that can bemade by stacking mattes corresponding to FIG. 2A. The composite articleillustrates mattes (e.g. 2022, 2023) can have different orientations,such as an orientation with each z axis parallel (heightwise stacked),and the fiber orientation of each immediately adjacent and contactingmatte being at right angles. If a matte is made by consolidating twothin mattes with fiber orientation stacked at right angles, such a matteor analogous mattes can be stacked with each z axis parallel (heightwisestacked), to obtain a composite article of FIG. 2B. Note that if a matteis made by consolidating two mattes with fiber orientation stacked atparallel to give a thicker matte, such a consolidated matte or analogousmattes can not, apparently, be stacked with each z axis parallel(heightwise stacked), to obtain a composite article of FIG. 2B.

FIG. 2C shows a portion of an oriented composite article 2030 that canbe made by stacking mattes corresponding to FIG. 2A (e.g., 2031 and2032). Note the grouping of pluralities of mattes into groups (2037,2039, 2035, where the plurality is a triplet of mattes). Some mattes areoriented parallel, some are oriented at right angles. This compositearticle shows a pattern of stacking that can be termed an orientationpattern of 0, 0, 0, 90, 90, 90 degrees.

A matte can be prepared by any known techniques. For instance, using apaper making process, fibers can be mixed with a polymer to form amixture or slurry. Any mixing means may be used, but preferably thefibrous components are mixed at about a 0.001% to 5% consistency orsolids content (e.g. comprising 0.01-5 parts solids to 99.009-95 partsaqueous solution or water). The slurry may then be diluted with water toenhance formation, and it may finally be flocculated with flocculatingagent and drainage retention aid chemicals. Then, the flocculatedmixture or slurry may be placed onto a paper making machine to be formedinto a wet matte, possibly with orientation of fibers or withoutorientation of the fibers, possibly oriented in the direction ofmovement of the matte during the paper making process, or perpendicularto that direction. Alternatively, the matte may be formed by vacuumcasting the slurry or other methods. Mattes can be formed by dewateringa slurry, for example using a belt press. A belt press manufacturer isBright Technologies, Hopkins, Mich. Mattes can be dried, for example inovens, on rotating drums, or by moving air. For a more detaileddescription of some standard paper making techniques that can beemployed, see U.S. Pat. No. 3,458,329, the disclosure of which isincorporated herein by reference.

Densifying can be carried out by compression or other known methods,which may be upon one or more axes, simultaneously or consecutively. Theaxes may be mutually orthogonal, such as x, y, and z axes.

Mattes may have any convenient dimensions of length, width, or height.Mattes can be more than 1 cm in height, or less than 0.8, 0.6, 0.4, 0.2,0.1, 0.05, or 0.01 cm in height.

Densification can be carried out at pressures as low as 100 kPa, and ashigh as 100 MPa, and at interval pressures between about 100 kPa andabout 100 MPa.

Densification, heating, cooling, or combinations of such can be carriedout from about 0.1, 1, 2, 5, 10, 20, 100 minutes or many hours, up toabout 135 hours, or more.

Any method of densifying can, and may, break at least some of the fibersduring processing. Accordingly the length of the fibers can be reduced.It is usually advantageous to maintain a high fiber length, but thisgoal may be advantageously compromised for certain applications if otherproperties of the consolidated composite article are improved.

A matte may be made by other means, such as dry air laying optionallywith polymer particles present. A matte may be densified by dryneedling. Some aspects of matte technology are presented in U.S. Pat.No. 6,855,298, the disclosure of which is incorporated herein byreference.

The polymer of the invention can be a fluoropolymer and any polymer ofthe invention can comprise repeat units or monomers oftetrafluoroethylene, perfluoro (alkoxyalkane) of 3 to 14 carbon atomssuch as perfluoro(vinyl propyl ether), hexafluoropropylene,chlorotrifluoroethylene, ethylene, propylene, or combinations thereof(copolymers).

Any polymer of the invention can optionally flow upon heating,particularly above the polymer melting point or glass transitiontemperature (Tg). The polymer can optionally wet the fibers,particularly after softening. In a copolymer of any collection ofmonomers, the content of any comonomer can vary from about 10 to 99weight percent of the polymer.

Any polymer of the invention can be a thermoplastic, a thermoset, ormixtures or blends thereof. Any polymer of the invention can becross-linkable or crosslinked. Any composition of the invention cancomprise a cross-linker.

Any repeat unit or monomer of the polymer can comprise 0.001 to 99.999weight percent of the polymer.

The softening temperature of the polymer is a temperature at which thepolymer can be slowly but permanently deformed typically withoutbreaking, chipping, or separating. Examples of the softening temperatureinclude the melting point, the lowest temperature of a melting range,the highest temperature of a melting range, or the glass transitiontemperature.

Particles are small pieces or parts, or tiny portions or flecks.Particles can be free-flowing or stuck to fibers. Types of particlesinclude flakes, grains, shreds, fragments, crumbs, chips, pellets,specks, shavings, etc.

Fibers include, but are not limited to, those composed of: glass;graphite; carbon; fluorinated graphite; aramid such aspoly(p-phenyleneterephthtalamide); boron nitride; silicon carbide;polyester; and polyamide. Carbon, graphite and fluorinated graphitefibers are preferred fibers. Fibers of the present disclosure can alsobe chopped.

The median length of the fibers can be longer or shorter or the same asthe median height of the matte containing the fibers.

Fibers may be sized as known in the art. Sizing may comprise, forexample, epoxy resins or polymers, urethane-modified epoxy resins orpolymers, polyester resins or polymers, phenol resins or polymers,polyamide resins or polymers, polyurethane resins or polymers,polycarbonate resins or polymers, polyetherimide resins or polymers,polyamideimide resins or polymers, polystylylpyridine resins orpolymers, polyimide resin, bismaleimide resins or polymers, polysulfoneresins or polymers, polyethersulfone resins or polymers, epoxy-modifiedurethane resins or polymers, polyvinyl alcohol resins or polymers,polyvinyl pyrrolidone resins or polymers, resins or polymers andmixtures thereof. Sizings may be solvent compatible or water compatible,and may be solvent soluble or water soluble. Polyvinylpyrrolidone (PVP),a known sizing agent, is a water-soluble polymer made from the monomerN-vinylpyrrolidone. Known sizing agents are disclosed in US Pub.20080299852; U.S. Pat. Nos. 5,393,822 and 7,135,516.

One process for the production of a polymer-fiber composite comprisesco-dispersing-thin polymer flakes having some irregular fibularstructure extending from an irregular periphery. The flakes, or theco-dispersed flakes and fiber in water, used to make a matte bypaper-making techniques, can have a Canadian Standard Freeness ofgreater than 200 up to the Freeness test maximum of 2000. The flakes, orthe co-dispersed flakes and fiber in water, used to make a matte bypaper-making techniques, can have settling times of from 1 to 13 000seconds or more. Settling time is measured, optionally with the fibercontent ratio by weight to be used in a matte, in an aqueous solution(i.e., less than 1% based on weight of polymer solids suitable to forman apparently homogeneous slurry appropriate for feeding to a screen toultimately form a matte, observed until such time a new layer is formedon the bottom or the top discernable to the naked eye). Settling timecan be greater than from about to 2 to about 12 000 seconds.

In any embodiment, removing most water from matte to form a wet matte;removing more water from the layer to form a dry matte; drying the layerto form a self-supporting planar matte; optionally thermally tacking theweb to improve dry strength for handling and preconsolidating said matteby heating said matte above the polymer melt temperature to form adifferent matte, then applying sufficient pressure normal to the planeof said matte to cause the polymer to flow to form a preconsolidatedmatte; and cooling that matte. The aqueous slurry can be substantiallyfree of other constituents.

The fiber content in the composite of the present invention is fromabout 1 to 90 weight percent fiber.

Suitable belt presses are well known, for example in U.S. Pat. Nos.3,159,526; 3,298,887; 4,369,083; 5,112,209; 5,433,145; 5,454,304;5,460,764, 5,520,530; 5,546,857; 5,555,799; 5,592,874; 5,759,927;5,895,546 each of which is hereby incorporated by reference in theirentirety. A manufacturer of suitable belt presses, particularly isobaricdouble belt presses, is Held Technologie GmbH, Germany. A manufacturerof double belt systems useful for fiber reinforced thermoplastics isBerndorf Band GmbH of Austria.

Suitable platen presses are well known, for example U.S. Pat. Nos.5,775,214, 5,253,571, 5,323,696 and 5,333,541 each of which is herebyincorporated by reference in their entirety. Manufacturers of suitablepresses include Maschinenfabrik Herbert Meyer GmbH in Germany (verticalpresses or laminating presses, e.g. models APV, Fusing Press AHV-Bm, orAHV-S with up to 20 tons pressure and heating plates up to 673 K).

Suitable methods of applying alternating stages of compression andheating are known, for example U.S. Pat. No. 6,287,410 each of which ishereby incorporated by reference in their entirety.

Suitable methods of applying heat include but are not limited tocontacting a matte or composite article with a hot surface (e.g.conduction); using a hot gas jet (e.g. convection); and using radiation(e.g. infrared or microwave radiation).

Densification methods are well known, for example in U.S. Pat. No.6,032,446 each of which is hereby incorporated by reference in theirentirety.

Consolidation can be carried out under the same conditions asdensification. In addition, heating to a temperature above the softeningtemperature or heating to a temperature below the softening temperature,or both in various combinations as known in the art, can be carried outoptionally as defined herein, during consolidation. Accordingly, one canmake a composite article of density Dc comprising polymer and fibers,said method comprising by providing a first matte. The first matte maybe a matter comprised of thin mattes. In either case the matte comprises1 to 91 weight percent fiber” and “9 to 99 weight percent polymer. Thefirst matte having a density of Dm is less than Dc.

The first matte is densified by compressing to a density greater than1.1 times Dm and less than 0.999 times Dc while at least a portion ofthe first matte is at a temperature less than said softeningtemperature. This will provide a compressed matte. Thereafter, thecompressed matte is heated throughout to a temperature greater than thesoftening temperature of the polymer, while at a consolidated densitygreater than 1.1 times Dm and less than 0.999 times Dc. This willprovide a preconsolidated matte, which is then cooled, or a least aportion is cooled to a temperature less than said softening temperatureof the polymer to provide a consolidated matte.

A plurality of consolidated matte is then stacked heightwise to providean unconsolidated article. The height of the unconsolidated article iscompressed and heated throughout to a temperature greater than thepolymer softening temperature, to provide a consolidated compositearticle. At least a portion of the consolidated composite article iscooled to a temperature less than the softening temperature of thepolymer.

Disclosed herein is a method for making an composite article withorientation, by preconsolidating said stack by: heating said stack toabove the melt temperature of the polymer, then applying sufficientpressure normal to the plane of the matte while the matte isunconstrained in the in-plane direction to cause the fluoropolymer toflow orienting the fibers in substantially the plane of the layer bymeans of said flow to form a preconsolidated sheet;

Composite articles can be used for chucks, for example spin chucks usedin coater chambers to hold wafers, or for CMP chucks for holding wafersor polishing pads during chemical mechanical polishing (CMP).Particularly preferred are chucks which are rotated about their z axisat high rates of speed, where strength in the x-y plane of the compositeallows higher diameters or higher rates of speed to be used, allowingfor larger chucks or larger wafers or faster processing or more robustprocessing. Also preferred in chucks are composites that resistdeformation, thereby holding the wafer in a planar position forprecision processing. Cleanliness (e.g. low metal content, low or slowelution of metal or ions) in composites is also prized in semiconductormanufacturing articles, including in spin, rinse, and dry modules andchucks. Composites are valued as a support structure for thesemiconductor wafer, e.g., such support structures also known as waferchucks, susceptors, or wafer pedestals. Semiconductor manufacturingarticles are well known, for example in U.S. Pat. No. 7,357,842;20090033898; 5,451,784; 5,824,177; 5,803,968; and 6,520,843 each ofwhich is hereby incorporated by reference in their entirety.

Composite articles are useful in sealing elements, for example incompressor valves as disclosed in U.S. Pat. No. 7,011,111; each of whichis hereby incorporated by reference in their entirety.

The present invention is useful in at least one, or a combination, of(including but not limited to): a simplified process of manufacture; arobust and/or reproducible process of manufacture that can producerobust and/or reproducible product; a process to produce an article ofincreased density; an article of increased density; a process to produceproducts having fewer metal, metallic, ionic, or related impurities,particularly for processes that include a solvent or water; a processfor using fibers that preserves fiber length; a process to produceproduct having a uniform property throughout a useful volume; anyprocess to produce a composite product having a directional property(such as tensile strength, compressive strength, or elongation to break)that is uniform or superior regardless of the direction of measurement(or uniform or superior in one direction, or uniform or superior in twoorthogonal directions), and the like.

A composite article of the invention can used for known applications,e.g. equipment for semiconductor manufacture, in aircraft parts, inautomotive parts, in gaskets, in seals, and the like. The article of thepresent invention may be a spin disk.

EXAMPLES

Materials similar to the following, and methods for making similarmaterials and articles, are detailed in U.S. Pat. No. 5,470,409 toDeakyne et al., issued Nov. 28, 1995, entitled “Process for makingfluoropolymer composites,” U.S. Pat. No. 5,232,975 to Deakyne, issuedAug. 3, 1993, entitled “Preconsolidation process for makingfluoropolymer composites,” U.S. Pat. No. 5,427,731 to Chesna et al.,issued Jun. 27, 1995, entitled “Compression molding of structures,” andU.S. Pat. No. 4,163,742 to Mansure, issued Aug. 7, 1979, entitled“Process and product prepared from tetrafluoroethylene polymer andgraphite fibers,” all of which are incorporated by reference in theirentirety.

In the following Examples, Teflon® PFA is a registered trademark of andavailable from E.I. du Pont de Nemours and Company, Wilmington, Del.,and can include a polymer containing about 99 mole percenttetrafluoroethylene and about 1 mole percent perfluoro(propyl vinylether).

A carbon fiber CF1 used was polyacrylonitrile based, had a length ofabout 6.0 mm, a diameter of about 5 to 7 microns, a bulk density ofapproximately 200 g/L, approximately 4 weight percent water compatiblesizing, a carbon density of approximately 1.8 g/cm3 by ASTM D1505, atensile strength of at least about 500 ksi (greater than 3450 MPa) andtensile modulus of at least approximately 31.6 Msi by ASTM D4018.Elemental analysis of the fiber for metal content in units of nanomolesper gram fiber showed results of approximately 170 000 for sodium, 770for potassium, 180 for calcium, and 22 for aluminum.

A similar fiber CF2 had lower content of metals. Elemental analysis ofthe fiber for metal content in units of nanomoles per gram fiber showedresults of approximately 830 for sodium, 510 for potassium, less than 10for calcium, and 3 for aluminum. Tensile strength was >500 ksi (>3.45GPa), tensile modulus was >30 Msi (>207 GPa), and the fiber appeared tobe somewhat stronger than CF1. The sizing level was 3.8 weight percent;the sizing was characterized as water soluble.

A fiber CF3 similar to CF2 in physical properties, also had content ofmetals similar to CF2, yet was essentially free of sizing.

A type of Teflon® PFA pellets PFAP1(tetrafluoroethylene-perfluoro(propyl vinyl ether) copolymer, CAS26655-00-5) have a melting point of approximately 305 C, a flow rate of14 g/(10 min) and tensile yield strength of approximately 13.8 MPa andtensile strength of approximately 25 MPa at 25 C and 12 MPa at 250 C byASTM D3307, and a specific gravity of approximately 2.15 g/mL.

PFA flakes (PFAF1) from PFAP1 were made using a disc mill of the typemanufactured by Andritz Sprout (Muncy, Pa.) as taught inPatent/Publication Number U.S. Pat. No. 5,506,052A by Deakyne.

A wet matte Mw1 was made from 20% by weight CF1 and 80% by weight PFAF1according to the methods of U.S. Pat. No. 5,506,052A.

The dry matte Md1 made from Mw1 (before notable compression of Mw1) hasa width of approximately 16.75 inches, a length of over 18 inches, and abasis weight of approximately 0.12 lb/ft2.

The coherent matte Mcg made from Md1 (before notable compression of Md1)has a thickness of approximately 0.095 inches (approximately 2.4 mm,2400 microns) and approximately the same basis weight.

A preconsolidated article CAp1-24 was made on a platen press from cutportions of coherent matte type Mc1. Squares of approximately 16.5inches were cut, making note of the original length direction.Approximately 24 squares were stacked one upon the other with the lengthdirections each orthogonally oriented to their one (for top or bottommatte) or two (for internal matte) nearest neighbors to produce a stackabout 2.2 inches thick. The stack at essentially ambient temperature wasplaced in a temperature-controlled platen press and heated so that thetemperature throughout the stack was greater than 310 C (583 K, 590 F)while the stack was minimally compressed along the thickness (z)direction at a pressure less than 90 psi (4310 Pa), while beingunconstrained by any added pressure in the length and width (x and y)directions. The completely heated stack was then further compressedalong the thickness direction while heating was ended and cooling wasbegun. The stack was thus consolidated to a thickness of about 0.285inches and the temperature was decreased throughout the article to lessthan 290 C (563 K, 554 F). Then the temperature of and pressure on thestack were reduced to ambient conditions to obtain the article CA1-24.

Articles CA2-24 and CA3-24 were made as for CA1-24 by substitution ofcarbon fibers CF2 and CF3 respectively for CF1. The wet matte Mw3incorporating CF3 (free of sizing) was notably different in processingand appearance compared to Mw1 and Mw2 incorporating CF2. The compositematerial made from the sized carbon fibers CF2 demonstrated superiortensile strength and appearance.

A heatable belt press HBP1 or HPB2 was used to make preconsolidatedmattes. HBP1 was a continuous dual belt press with a working width ofabout 30 inches and a working length of about 10 feet. The constant gapworking height was adjustable. The belt press temperature was adjustablein multiple zones.

In run BP1, the entrance zones of HBP1 were set to 500 F, the internaltransport zones were set to 700 F, and the later cooling zones withinthe working length were cooled by water entering the zones atapproximately 32 F and exiting the final cooling zone at less than 100F. The gap between the two belts was set to about 0.028 inches asmeasured the thickness after exit by a length of solder passed throughthe press. Both belts were coated by a release formulation. A singlesheet of matte about 0.095 inches in height was passed through the pressto continuously produce a preconsolidated matte about 0.015 inches inheight. The matte was fed into the belt press at 12 inches per minute.In trial BP2, the feed rate of matte was increased to 15 inches perminute.

In trial BP3, three mattes were continuously and simultaneously fed intothe belt press while aligned with their lengths parallel. The gapbetween the two belts was approximately 0.084 inches, and thepreconsolidated matte height was approximately 0.045 inches. Feed ratewas 12 inches per minute. Analogously in BP4, five mattes werecontinuously and simultaneously fed into the belt press while alignedwith their lengths parallel. The gap between the two belts wasapproximately 0.10 inches, and the preconsolidated matte height wasapproximately 0.075 inches. Feed rate was 12 inches per minute.

The preconsolidated mattes from each belt press process (BP1-4, etc.)were separately cut into portions, assembled mutually orthogonally intostacks as for the platen-press-made material, and finally compressed asfollows.

A final compression of stacks of preconsolidated mattes were made toachieve final products about 6.5 inches in height.

Preconsolidated matte made on the platen press at a density of 1.85 g/mLhas been noted to expand so as to lower its density to about 1.4 g/mLduring heating to above 300 C while restrained by [80 tons on 16 sqinch]. Preconsolidated matte made on the constant gap belt press had adensity of about 1.4 g/mL and did not undergo noticeable expansionduring heating to 300 C while restrained by the same pressure. Finaldensification was higher in the case of reconsolidated matte made on theconstant gap belt press under identical conditions of exposed pressureand temperature profiles in the article press.

A composite article can a coefficient of thermal expansion in the XYdirection of about 10 ppm/K; the coefficient of thermal expansion in theZ direction can be greater or less than in the XY direction.

All parts are by mass unless otherwise noted.

1. A consolidated composite article having a density, Dc, andcomprising: (i) a polymer having a softening temperature and (ii)fibers, said composite article produced by: providing a matte, whereinsaid matte is a mixture comprising: from about 1 wt % to about 90 weightpercent of said fibers; and from about 10 weight percent to about 90weight percent particles of a polymer, said matte having a density, Dm,that is less than Dc; densifying said matte to a compressed densitygreater than 1.1 times Dm and less than 0.999 times Dc while at least aportion of said matte is at a temperature less than softeningtemperature of polymer, to provide a compressed matte; heating saidcompressed matte throughout to a temperature greater than said softeningtemperature at a density greater than 1.1 times Dm and less than 0.999times Dc, to provide a preconsolidated matte; cooling at least a portionof said preconsolidated matte to a temperature less than said softeningtemperature, to provide a consolidated matte; stacking a plurality ofsaid consolidated matte to provide an article having fiber orientationof each immediately adjacent and contacting matte at right angles;compressing the height of said article and heating throughout to atemperature greater than said softening temperature, to provide aconsolidated composite article; and cooling at least a portion of saidconsolidated composite article to a temperature less than said softeningtemperature.
 2. The composite article of claim 1 wherein said polymer isselected from fluoropolymer or polymers comprising repeat units ormonomers of tetrafluoroethylene, perfluoro (alkoxyalkane) of 3 to 14carbon atoms.
 3. The composite article of claim 2 wherein said polymeris selected from the group consisting of perfluoro(vinyl propyl ether),hexafluoropropylene, chlorotrifluoroethylene, ethylene, propylene, andcombinations thereof.
 4. The composite article of claim 1 wherein saidpolymer comprises (tetrafluoroethylene-perfluoro(propyl vinyl ether)copolymer.
 5. The composite article of claim 1 wherein said fibers areselected from the group consisting of glass, graphite, carbon;fluorinated graphite; aramid, boron nitride; silicon carbide; polyester;and polyamide.
 6. The composite article of claim 1 or 4 wherein saidfibers are chopped fibers.